1. Field of the Invention
The present invention is related to the field of bone dowels, and more specifically devices and method designed to be used (e.g., in a sterile setting) to manufacture a bone dowel for use in spinal surgery.
2. Description of the Related Art
Clinical spinal fusion procedures using bone graft have been used for decades. Anterior cervical interbody fusion using cylindrical smooth bone grafts as spacers was reported by several authors by the mid-1950""s. In 1985, threaded cylindrical bone dowels were reported by Vich, eliminating the need to hammer the dowels in place. In the use of these dowels, a cylindrical bed was drilled in the appropriate intervertebral bodies and the graft was then screwed into the opening. Bone grafts could be attained from iliac crests as described by Cloward or using a Kiel-surgibone heterologous graft. Threaded dowels were prepared with a sterilized die or with a small lathe.
U.S. Pat. No. 5,814,084 describes cortical bone dowels derived from cortices of bone diaphyses that may have a chamfered insertion end. The dowels described in the ""084 patent may also include a canal derived from the intramedullary space of a diaphysial bone that retains the natural architecture of that region of the bone, and which can be packed with cancellous bone. The background section of the ""084 patent provides a discussion of the development of the art. The ""084 patent is incorporated herein by reference.
A device for manufacturing a bone dowel may include a machine base with one or more tracks in a surface thereof. In some embodiments, at least one track may be perpendicular to at least one other track. In this configuration, the machine base may include at least one perpendicular intersection of two or more tracks. The device may also include a rotary cutting tool module, configured to hold a rotary cutting tool and to slide in a track in the machine base. The device may also include one or more modules for holding a dowel, preferably configured such that the modules are configured to slide in the tracks in both parallel and perpendicular orientation to a rotary cutting tool module disposed in a track during use, thus enabling an operator to perform various cutting, drilling and milling operations on a dowel.
As is described herein, one or more modules may slide in the tracks in perpendicular or parallel orientation to a cutting tool during use. Although embodiments are described in which a machine base includes two tracks in perpendicular orientation, a machine base may also include two, three, or more tracks perpendicular to one or more tracks that may be configured to hold a cutting tool module, for example. In this way, more than one dowel module may be disposed on the machine base simultaneously or even sequentially in different tracks as needed to contact one or more cutting tools.
In one embodiment, a device for manufacturing a bone dowel in which a rotary cutting tool may be held in an appropriate position, and a module holding a dowel may be moved relative to the cutting tool in order to contact the rotary tool and shape the dowel to the desired size and configuration is described. In other embodiments, both the cutting tool and the dowel are held in modules that slide in tracks for controlled positioning and machining of the dowel. Other embodiments may include only one track, and a module holding a bone dowel may contain a sliding member configured to allow the dowel to be moved perpendicular to the cutting tool held in a module mounted in the track.
The devices disclosed herein offer certain advantages over more conventional dowel manufacturing devices, such as lathes, in which a motor is connected to a shaft or other device configured to turn the dowel, and an operator then contacts the dowel with a knife, a gouge, or other stationary tool. Dowels made on such a device are typically machined to size in a clean room and then a number of different sizes are packaged and frozen. A surgeon typically thaws a number of different sizes of dowels so that one can be chosen during surgery to best fit the need of the patient. Unfortunately, the dowels that are not used cannot be re-frozen and must be discarded. The devices disclosed herein, in contrast, can be used in the operating room during surgery. The use of high speed rotary cutting tools is, in fact, routine in certain surgical procedures in operating rooms and the present device is adaptable to those rotary cutting tools. The present devices, then, may be sterilized and used in surgery to produce a dowel of the needed size from a dowel blank, after the surgeon has determined the needed size. This reduces waste of human tissue and unnecessary expense, since only the single dowel blank need be thawed, rather than a selection of pre-sized dowels.
The terms dowel, bone dowel, dowel blank, and bone portion are interchangeably used to describe a portion of bone that has been cut from donor bone and is ready for, or in the process of, being manufactured using the devices described herein. The terms dowel and bone dowel may be used to describe the finished product of the manufacturing process.
In certain embodiments, the modules for holding a dowel include a collet module, including a base configured to slide in a track and a collet configured to hold a dowel such that an end of the dowel may contact the cutting tool during use. A collet may be configured to hold a dowel by one end such that the opposite end may contact the cutting tool. As used herein, a dowel may typically be cylindrically shaped, such that the dowel is defined by two ends separated by the height of the dowel. The height may also be described as the long axis of the dowel, and the circumference of the long axis as the circumferential portion of the dowel. A collet module may be configured to hold a dowel parallel to the base of the module, or perpendicular to the base. As described herein, parallel means that the long axis of the dowel is parallel with the track in which the base is held during use. In some embodiments, a collet module may be useful to machine an end of a dowel smooth by moving a dowel in a track perpendicular to the rotary cutting tool until an end contacts the cutting tool burr. The dowel may then be manually rotated to achieve a smooth end. The collet module may also be useful for drilling a center hole in an end of a dowel by moving the dowel held in the collet module in parallel orientation to a drill bit mounted on a rotary cutting tool held in a rotary tool module. Alternately, a center hole may be drilled in an end of a dowel held in the collet module by moving a rotary tool module holding the drill bit or burr mounted on a rotary cutting tool in parallel orientation to the collet module.
The modules for holding a dowel may also include a vise module including a base configured to slide in a track and a vise configured to hold a dowel along the length thereof such that an end of the dowel may contact a cutting tool during use. In some embodiments, a vise module may include a base configured to be mounted in a track and a vise configured to hold a dowel mounted on a sliding member configured to slide on the base perpendicular to the track. A vise module may include an opposed pair of jaw members configured to move together to press against an object held between the jaw members. In some embodiments, vise modules may include a groove or indention in one or both jaw members configured to conform to the circumferential portion, or the sides of the long axis of a dowel. The module may preferably be configured to hold a dowel perpendicular to the base such that an end of the dowel is free to be machined during use. The vise module may also be configured to hold a dowel securely against a force resulting from a cutting tool traveling across the face of an end and from a force resulting from a drilling tool boring into the face of an end. The vise module may be useful in cutting a groove or slot into an end of a dowel. Such a groove or slot may be useful for interacting with a chuck coupled to a module during the manufacturing process, orienting a dowel during surgery, or for interacting with a tool used to insert the dowel into a spine. As such, a dowel held in the vise module may be moved in a track perpendicular to a cutting tool to machine such a groove or slot during use. The vise module may also be useful for drilling a center hole in an end of a dowel by moving a dowel held in the vise module in parallel orientation to a drill bit or burr mounted on a rotary cutting tool held in a rotary tool module. Alternately, a center hole may be drilled in an end of a dowel held in the vise module by moving a rotary tool module holding the drill bit or burr mounted on a rotary cutting tool in parallel orientation to the vise module.
A device for manufacturing a bone dowel may also include a threading module including a base configured to slide in a track, a dead center, and a chuck opposed to the dead center, configured to hold a dowel by the ends such that a cutting tool may contact the circumferential portion of the dowel during use. In certain embodiments, the chuck may be configured to hold the dowel by one end and may provide a mechanism for turning or rotating the dowel around its long axis. In other embodiments, a dead center is provided that may engage a center hole drilled in the opposite end of a dowel during a previous step in manufacture, and the dead center may be spring loaded to hold the dowel in the module during use. In some embodiments, a coil spring is used, but other spring configurations may also be used to bias the dead center toward the chuck of the module.
In certain embodiments, a device for manufacturing a bone dowel may include a support member coupled to the machine base in a track, wherein the support member includes a threaded opening. The support member may be disposed at an end of a track that is perpendicular to a track holding a cutting tool module, or it may be disposed anywhere in a perpendicular track, or even in parallel orientation to the cutting tool module. The threaded opening may be configured to engage a threaded projection included on certain modules, configured such that turning the threaded projection in the threaded opening is effective to move the module in the track. In this way an operator has better control of the module than is possible with a free-hand movement of the module. For example, a collet module may include a threaded projection configured to threadably mate with the threaded opening such that turning the threaded projection is effective to move the collet module in the track. The collet module may also include a knob coupled to the threaded projection configured so that turning the knob turns the threaded projection. The knob coupled to the threaded projection may include marks configured so that rotating the knob from one mark to a second mark relative to a fixed position moves the module a known distance in the track. In certain embodiments, a threading module may also include a threaded projection configured to threadably mate with the threaded opening such that turning the threaded projection is effective to move the threading module in the track, and to turn a dowel held in the threading module. In this way, an operator may make more than one pass with the threading module while maintaining the starting point and pitch in order to cut threads into a dowel. This embodiment makes it easy to return to the start of a thread. The pitch of the threaded opening also determines the pitch of the threads cut on a dowel.
The module for holding a rotary cutting tool as used in any of the described devices may be disposed in a track and may include an arm rigidly coupled to the module and configured to threadably engage a threaded rod. In certain embodiments, a threaded rod may be provided and disposed parallel to the track holding the rotary cutting tool module. In some embodiments, the rod is rotatable and may be held in one or more support members coupled to the machine base. In this configuration, turning the rod is effective to move the cutting tool module in the track. A knob may be coupled to the rod to aid an operator in turning the rod. The knob coupled to the rod may include marks configured so that rotating the knob from one mark to a second mark relative to a fixed position moves the rotary cutting tool module a known distance in the track. Any of the devices described herein may further include a high speed rotary cutting tool.
Described herein are also methods of manufacturing a bone dowel. Methods may include: providing a machine base including two or more tracks, wherein at least one track is perpendicular to at least one other track; providing a rotary cutting tool module in a first track and further providing a rotary cutting tool held in the module; providing one or more modules for holding a dowel, wherein the modules are configured to slide in the tracks in both parallel and perpendicular orientation to the first track; providing a bone dowel; moving the bone dowel past the cutting tool and in contact with a burr mounted on the cutting tool by sliding a module holding the dowel past the cutting tool when the module is in a second track, perpendicular to the first track, by sliding a module toward the cutting tool when the module is in the first track, or by sliding a sliding member of a module for holding a dowel past the cutting tool while the module is in the first track; moving a burr mounted on a cutting tool to contact the dowel by sliding a module holding the cutting tool toward a module holding the dowel when the module holding the dowel is in the first or second track. In some embodiments, the modules for holding a dowel may include a collet module including a base configured to slide in a track and a collet configured to hold a dowel such that an end of the dowel may contact the cutting tool during use; a vise module including a base configured to slide in a track and a vise configured to hold a dowel along the length thereof such that an end of the dowel may contact a cutting tool during use; and a threading module including a base configured to slide in a track, a dead center, and a chuck opposed to the dead center, configured such that a dowel held in the threading module may contact a cutting tool while rotating around the long axis of the dowel during use.
Methods may also include providing a support member coupled to the machine base in a track, wherein the support member includes a threaded opening, and may further include providing a support member including a threaded opening coupled to the machine base in a track, wherein the collet module includes a threaded projection configured to threadably mate with the threaded opening such that turning the threaded projection is effective to move the collet module in the track, and wherein the vise module includes a threaded projection configured to threadably mate with the threaded opening such that turning the threaded projection is effective to move the vise module in the track. In addition, some embodiments may include providing a support member including a threaded opening coupled to the machine base in a track, and wherein the threading module includes a threaded projection configured to threadably mate with the threaded opening such that turning the threaded projection is effective to move the threading module in the track, and to turn a dowel held in the threading module. In the practice of some embodiments, the module for holding a rotary cutting tool may be disposed in a track and include an arm rigidly coupled to the module and configured to threadably engage a threaded rod, wherein the rod may be disposed parallel to the track and may be rotatable in one or more support members coupled to the machine base such that turning the rod may be effective to move the module in the track.
Some embodiments of manufacturing a bone dowel as described herein may also include placing a collet module in a second track, perpendicular to a first track, and securing the bone dowel in the collet module; mounting a cutting tool burr on the cutting tool; moving the cutting tool module to position the cutting tool burr parallel with the end of the dowel; moving the collet module to contact the cutting tool burr effective to smooth the first end of the dowel; repositioning the dowel in the collet and moving the collet module to contact the cutting tool burr effective to smooth the second end of the dowel; mounting a bit in the cutting tool; moving the collet module to the first track; moving the collet module to contact the cutting tool bit effective to drill a centered hole in the end of the dowel; repositioning the dowel in the collet and moving the collet module to contact the cutting tool burr effective to drill a centered hole in the opposite end of the dowel.
The methods may also include: mounting a cutting tool burr in the cutting tool; placing a vise module in a track perpendicular to the first track; securing the dowel in the vise module; moving the cutting tool module to position the cutting tool burr parallel with the end of the dowel; moving the vise module past the cutting tool effective to machine a groove in an end of the dowel. The methods may also include mounting a threading burr on the cutting tool; placing a threading module in a track perpendicular to the first track; mounting the dowel in the threading module; positioning the modules so that the burr contacts the dowel near one end thereof; and simultaneously turning the dowel and sliding the threading module past the cutting tool effective to thread the dowel.
Other embodiments of manufacturing a bone dowel may include placing a vise module in a first track, and securing the bone dowel in the vise module; mounting a cutting tool burr on the cutting tool; moving the cutting tool module to position the cutting tool burr parallel with the end of the dowel; moving the vise module to contact the cutting tool burr effective to smooth the first end of the dowel; repositioning the dowel in the vise and moving the vise module to contact the cutting tool burr effective to smooth the second end of the dowel; mounting a bit in the cutting tool; moving the vise module to contact the cutting tool bit effective to drill a centered hole in the end of the dowel; repositioning the dowel in the vise and moving the vise module to contact the cutting tool burr effective to drill a centered hole in the opposite end of the dowel; mounting a cutting tool burr in the cutting tool; moving the cutting tool module to position the cutting tool burr offset from the center of the end of the dowel mounted in the vise module; moving the vise module towards the cutting tool effective to machine a starting hole in an end of the dowel; moving the dowel mounted in the vise module perpendicular to the cutting tool module effective to machine a groove on the end of the dowel from the starting hole, across the center of the dowel, to a position opposed to the starting hole. The methods may also include mounting a threading burr on the cutting tool; placing a threading module in a track perpendicular to the first track; mounting the dowel in the threading module; positioning the modules so that the burr contacts the dowel near one end thereof; and simultaneously turning the dowel and sliding the threading module past the cutting tool effective to thread the dowel.
Also disclosed herein are methods of manufacturing a device for manufacturing a bone dowel, including: manufacturing a machine base including two or more tracks, wherein at least one track is perpendicular to at least one other track; manufacturing a rotary cutting tool module, wherein the module is configured to hold a rotary cutting tool and to slide in a track; and providing one or more modules for holding a dowel, wherein the modules are configured to slide in the tracks in both parallel and perpendicular orientation to a rotary cutting tool module disposed in a track during use. In some embodiments, the modules for holding a dowel may include a collet module including a base configured to slide in a track and a collet configured to hold a dowel such that an end of the dowel may contact the cutting tool during use; a vise module including a base configured to slide in a track and a vise configured to hold a dowel along the length thereof such that an end of the dowel may contact a cutting tool during use; and a threading module including a base configured to slide in a track, a dead center, and a chuck opposed to the dead center, configured such that a dowel held in the threading module may contact a cutting tool while rotating around the long axis of the dowel during use.
The present disclosure also includes bone dowels manufactured by the methods and/or utilizing the devices described herein. Such dowels may also include dowels in which the canal formed by the intramedullary space has been improved by the removal of cancellous bone to promote better bone grafting of a dowel to the adjacent vertebrae.
Embodiments of a bone dowel as described herein may include a slot machined in an end of the bone dowel so that the perimeter of the slot does not substantially violate the outer edge of the end of the bone dowel. The slot may be useful for interacting with a chuck coupled to a module used to hold or rotate the bone dowel during the manufacturing process, orienting a dowel during surgery, or for interacting with a tool used to insert the dowel into a spine. In some embodiments, the slot may be completely enclosed by the bony material at the end of the dowel and may be between 1 and 1.5 millimeters deep. In other embodiments, the slot may have rounded comers. In yet other embodiments, there may be a plurality of slots in the end of the dowel. The slot may be in a number of shapes, including, but not limited to, a rectangle with rounded comers, a cross, a hexagon, and an oval.
Some embodiments of a bone dowel may also include threads with radiused edges at the top of the threads and radiused corners at the base of the threads, and with substantially flat surfaces between the edges and comers. The term radiused as used herein describes a thread profile wherein the angular edges and comers of the threads have been smoothed to a substantially circular form. In some embodiments, the threads may be rounded into a sinusoidal shape. The term sinusoidal as used herein describes a thread profile that is continuously curved or radiused at all points. In other embodiments, the threads may have radiused edges at the top of the threads and angular comers at the bottom of the threads.
In some embodiments of a bone dowel a hole is drilled in an end of the dowel. A bone dowel may include a hole drilled in both ends of the dowel. The holes may be substantially centered on the ends of the dowel. The holes may include internal threading. The holes may extend from the ends of the dowel to the canal formed by the intramedullary space. In an embodiment, the holes may have a diameter approximately 10% that of the bone dowel, and the holes may be drilled through both ends of the bone dowel into the canal space, with internal threading in at least one of the hole extending about 50% from the slotted end of the bone dowel to the inner surface.
A bone dowel may be manufactured from sections of human long bones, with the intramedullary space oriented so as to form the canal of the bone dowel, and the cancellous bone material removed from the canal with, for example, a burr or file. Alternatively, a bone dowel may be manufactured from the long bones of other species, for example bovine, sheep, and pig, wherein the long bones are of sufficient dimensions to produce bone dowels of the required sizes. In another embodiment, a bone dowel may be manufactured from bones with sufficient dimensions and strength to produce bone dowels of the required size but lacking a natural canal such as the intramedullary space of a long bone. In these embodiments, the canal may be machined through the bone dowel.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described.